This application claims the priority right under Paris Convention of Japanese Patent Application No. 2000-245977 filed on Aug. 14, 2000, the entire disclosure of which is incorporated herein by reference.
(i) Field of the Invention
The present invention relates to magnetic recording media such as hard disks incorporated in external storage devices of computers, particularly to magnetic recording media with high coersive force and low noise in which a pre-coat layer for decrease in size of crystal grains of an underlayer and a magnetic layer and for suppressing dispersion of grain size of an underlayer and a magnetic layer is provided between a substrate and the underlayer, and manufacturing methods thereof.
(ii) Description of the Related Art
As a magnetic recording medium of this kind, for example, a magnetic recording medium as described in the specification of Japanese Patent Application No. 11-094391, which is a prior application of the present applicant, has been proposed. This magnetic recording medium is constructed by sequentially laminating, on a substrate, a seed layer in which an intermediate layer is interposed between at least two or more layers of non-magnetic films, a Cr or Cr-alloy underlayer, a Co-alloy magnetic layer, and attains high coersive force and low noise.
The high coersive force of this magnetic recording medium is attained by the manner that the seed layer enhances the crystal orientation of (110) plane in the body center cubic (bcc) of the Cr or Cr-alloy as the underlayer, and the crystal orientation of (100) plane in which the magnetization easy axis (c axis) of the Co magnetic layer epitaxial-grown thereon becomes parallel in plane is improved.
Besides, in this magnetic recording medium, since the film thickness of the underlayer can be thinned by providing the seed layer, by thinning the underlayer, Co magnetic grains thereon are made fine, and since the magnetization transition region (magnetic wall width) between recording bits can be decreased, noise can be reduced.
In recent years, development of magnetic recording media in which noise is reduced attendant upon still higher recording density of magnetic recording media and S/N ratio is improved is desired.
Although the crystal grain diameter of the magnetic layer must be decreased as fine as possible, if the crystal grain diameter of the magnetic layer is made very fine, there is a problem that a phenomenon in which the magnetization becomes thermally unstable, the recorded signal is attenuated with time, and finally the recorded signal disappears, that is, a phenomenon called thermal fluctuation occurs. Noise and thermal fluctuation are in relation of trade-off, and as the crystal grain diameter of the magnetic layer is decreased, although noise is reduced, the signal attenuation by the thermal fluctuation becomes large, and the recorded signal becomes easy to be attenuated with time or disappear. If the thermal fluctuation occurs, other than the signal attenuation (reduction of reproduction output), medium noise increases and the value of PW50 value (half pulse width of isolated reproduction signal) is deteriorated.
As a fine structure of a medium desired for high-density recording, it has become impossible that, as well as decreasing the crystal grains of the magnetic layer, the dispersion of grain size (grain diameter distribution) is decreased and generation of excessively fine grains apt to receive influence of thermal fluctuation is suppressed.
Because the crystal structure of the magnetic layer is obtained by taking over the crystal structure of the underlayer, as well as making the crystal grains of the underlayer still finer, the grain diameter distribution must be made small.
The present inventor and so on have made the present invention as a result of repeating earnest examination based on knowledge whether or not decrease in crystal grain of the magnetic layer and improvement of the dispersion of grain size can be intended by interposing a pre-coat layer between a substrate and the underlayer.
Accordingly, it is an object of the present invention to provide magnetic recording media with high coersive force, hard to receive the influence of thermal fluctuation, and bringing about considerable improvement of S/N ratio.
The present invention has the following constitutions.
A magnetic recording medium in which at least an underlayer and a magnetic layer are sequentially formed on a substrate, wherein a pre-coat layer for decrease in size of crystal grains of the underlayer and magnetic layer and for suppressing dispersion of grain size of the underlayer and magnetic layer is interposed between said substrate and the underlayer, and in said pre-coat layer, a lower layer containing Ni and P and an upper layer made of a Cr alloy are sequentially laminated from said substrate side.
The magnetic recording medium according to construction 1, wherein the crystal structure of said pre-coat layer is an amorphous structure or an almost amorphous structure.
The magnetic recording medium according to constitution 1 or 2, wherein said pre-coat layer contains nitrogen.
The magnetic recording medium according to constitution 3, wherein said nitrogen is contained at 1 to 20 at %.
The magnetic recording medium according to any one of constitutions 1 to 4, wherein said upper layer is a Cr alloy containing Cr and one of Zr and W.
The magnetic recording medium according to any one of constitutions 1 to 5, wherein a seed layer for controlling the crystal grain diameter of the underlayer and magnetic layer is formed between said pre-coat layer and the underlayer.
The magnetic recording medium according to any one of constitutions 1 to 6, wherein the film thickness of said lower layer is 50 to 2000 xc3x85.
The magnetic recording medium according to any one of constitutions 1 to 7, wherein the film thickness of said upper layer is 5 to 300 xc3x85.
The magnetic recording medium according to any one of constitutions 1 to 8, wherein said substrate is a glass substrate.
The magnetic recording medium according to any one of constitutions 1 to 9, wherein said magnetic recording medium is used under conditions of a linear recording density of 300 kfci or more.
A manufacturing method of a magnetic recording medium made by sequentially forming at least an underlayer and a magnetic layer on a substrate by sputtering, wherein a pre-coat layer having a lower layer containing Ni and P and an upper layer made of a Cr alloy is sequentially formed by sputtering between said substrate and the underlayer.
The manufacturing method of a magnetic recording medium according to constitution 11, wherein said pre-coat layer is sputtered in a mixture gas atmosphere containing an inert gas and nitrogen.
The manufacturing method of a magnetic recording medium according to constitution 12, wherein the content of nitrogen contained in the mixture gas is set at 20 to 80%.
The manufacturing method of a magnetic recording medium according to any one of constitutions 11 to 13, wherein said substrate is a glass substrate.
According to the above constitution 1, the pre-coat layer is constituted by the lower layer containing Ni and P and the upper layer made of the Cr alloy. The layer of the lower layer containing Ni and P has a role for interrupting organic pollution substances on the substrate surface or alkali impurities immersed out from the substrate, and a role for canceling (interrupting a film formed thereon so as not to influence the crystal growth) a surface state (such as the crystal structure) of the substrate surface. To the layer of the lower layer containing Ni and P, another element can be added without departing from the above effect. For example, Al, B, Zr, Ti, or the like, can be mentioned. The contents of these elements are preferably suppressed to 50 at % or less. Besides, the content of P (phosphorus) contained in the lower layer is preferably 10 to 30 at % for having the above effect.
The layer of the upper layer made of the Cr alloy has a work of an initial growth film of a film formed thereon. To have the work of the initial growth film, as an element added to Cr, at least one selected out of Zr, Nb, W, V, Ti, Mo, Ta, Ni, and Hf can be selected. The material containing Cr and the above element can obtain a fine crystal grain diameter and has a nature that the grain diameter distribution becomes very small. Accordingly, with avoiding an influence of thermal fluctuation, S/N ratio can be considerably improved as about 2 to 4 dB, and an improvement of PW 50 value (half pulse width of isolated reproduction signal) can be intended. Like the above description, to the Cr alloy of the upper layer, another element can be added without departing from the above effect. For example, B, C, O, or the like can be mentioned. The contents of these elements are preferably suppressed to 10 at % or less. Besides, the above element (at least one element selected out of Zr, Nb, W, V, Ti, Mo, Ta, Ni, and Hf) contained in the upper layer is preferably 10 to 50 at % for having the above effect.
Besides, the above pre-coat layer is important to have a laminate structure of the lower layer and the upper layer, and if it is a single layer of the lower layer, S/N ratio is improved by only about 0.8 dB, and if it is a single layer of the upper layer, it is improved by only about 0.3 dB, but by making a laminate structure of the lower layer and the upper layer, a considerable improvement of about 2 to 4 dB can be obtained.
Besides, in the above pre-coat layer, a middle layer may be provided between the lower layer and the upper layer if it is within a range without departing from the considerable improvement effects of these S/N ratios.
As in the above constitution 2, the crystal structure of said pre-coat layer is an amorphous or an almost amorphous structure. Here, an amorphous, an almost amorphous structure indicate a state that there is no definite X-ray diffraction peak or the X-ray diffraction peak is extremely broad when measuring with an X-ray diffract meter. To obtain such a crystal structure, nitrogen is contained in the pre-coat layer (lower layer, upper layer). Nitrogen has a work for make crystal grains fine, and a role for drawing out the above effect. The content of nitrogen contained in the pre-coat layer is preferably 1 to 20 at %. In case of less than 1 at %, since the effect of decrease in size is eliminated, it is undesirable, and if it exceeds 20 at %, since the film deposition (sputtering) speed is remarkably lowered, it is undesirable, and preferably, it is desirable to be 3 to 20 at %.
Incidentally, the deposition method of the pre-coat layer is not particularly limited. For example, a sputtering method, a vacuum vapor deposition method, a CVD method, or the like can be mentioned.
Besides, as in the above constitution 5, by setting the Cr alloy of the upper layer to a material containing Cr and one of Zr and W, since decrease in size of crystal grains and uniformization of grain diameter can be further intended, it is preferable on the point of noise reduction, improvement of PW 50 value, and resistivity of thermal fluctuation.
Besides, as in the above constitution 6, by forming the seed layer for controlling the crystal grain diameter of the underlayer and magnetic layer between the pre-coat layer and the underlayer, the uniformization of crystal grain diameter is further promoted, and since S/N ratio and resistivity of thermal fluctuation are improved, it is desirable. There is not particularly a limit in the material of the seed layer. For example, NiAl, AlCo, FeAl, FeTi, CoFe, CoTi, CoHf, CoZr, NiTi, CuZn, AlMn, AlRe, AgMg, CuSi, NiGa, CuBe, MnV, NiZn, FeV, CrTi, CrNi, NiAlRu, NiAlW, NiAlTa, NiAlHf, NiAlMo, NiAlCr, NiAlZr, NiAlNb, Al2FeMn2, or the like can be mentioned.
Besides, as in the above constitution 7, the film thickness of the lower layer is preferably set at 50 to 2000 xc3x85. More preferably, it is desirable to set at 300 to 1500 xc3x85. In case of less than 50 xc3x85, it is undesirable because it is influenced by pollution substances of the substrate surface, and the effect of canceling (interrupting a film formed thereon so as not to influence the crystal growth) a surface state (such as the crystal structure) of the substrate surface is eliminated, and uniformization of crystal grain diameter distribution of the initial growth film of the upper layer is not obtained, and if it exceeds 2000 xc3x85, it is undesirable because the crystal grain diameter of the lower layer becomes large, and by influence of it, also the crystal grain diameter of the magnetic layer becomes large, and S/N ratio is lowered. Besides, because the film stress of NiP becomes large, and the adhesion strength of the upper layer is lowered, it is undesirable. The relation between the film thickness and S/N ratio has a peak of S/N ratio between 300 to 1500 xc3x85 though the peak of S/N ratio changes by the material of the magnetic layer.
Besides, as in constitution 8, the film thickness of the upper layer is preferably set at 5 to 300 xc3x85. More preferably, it is desirable to set at 15 to 200 xc3x85. In case of less than 5 xc3x85, it is undesirable because the film is extremely thin and the effect of the above-described upper layer does not act, and if it exceeds 300 xc3x85, it is undesirable because the crystal grain diameter becomes large, and by influence of it, also the crystal grain diameter of the magnetic layer becomes large, and S/N ratio is lowered. The relation between the film thickness and S/N ratio has a peak of S/N ratio in the vicinity of 30 xc3x85 irrespective of the material of the magnetic layer.
Besides, in the magnetic recording medium of the above-described present invention, there is not particularly a limit in the material of the substrate. For example, a glass substrate (including a crystallized glass substrate), an aluminum alloy substrate, a ceramics substrate, a carbon substrate, a silicon substrate, or the like can be used. Among them, as in the constitution 9, in case that the substrate material is a glass substrate (including a crystallized glass substrate), since glass has an amorphous structure, the affinity with the film containing Ni and P of the amorphous structure of the lower layer is good, and the segregation of crystal with Ni and P is eliminated. As the glass kind of the glass substrate, aluminosilicate glass, soda lime glass, aluminoporosilicate glass, porosilicate glass, crystallized glass, quartz glass, or the like can be mentioned.
Besides, as in the constitution 10, the magnetic recording medium of the present invention is particularly useful in case of being used under conditions of a linear recording density of 300 kfci or more. To make the magnetic recording medium higher density, it is in general to raise the linear recording density and the track recording density. In recent years that higher density recording and reproduction are required, it is very meaningful that it is a medium (magnetic disk) with high linear recording density and good characteristics, and the magnetic recording medium of the present invention particularly shows an effect in an environment of using in high density recording and reproduction of such a linear recording density of 300 kfci.
Besides, as in the constitution 11, the manufacturing method of a magnetic recording medium of the present invention is a manufacturing method of a magnetic recording medium made by sequentially forming at least an underlayer and a magnetic layer on a substrate by sputtering, wherein a pre-coat layer having a lower layer containing Ni and P and an upper layer made of a Cr alloy is sequentially formed by sputtering between said substrate and the underlayer. By forming the pre-coat layer by sputtering, it is because an amorphous phase containing high purity Ni and P can be formed with a uniform film thickness. As for conditions (substrate temperature, gas pressure, film deposition time, and so on) upon sputtering, it is performed with being properly adjusted.
Besides, as in the constitution 12, by sputtering the pre-coat layer in the mixture gas atmosphere containing an inert gas and nitrogen gas, nitrogen can uniformize with decrease in size of crystal grain diameter of the pre-coat layer. Within a range without departing from the effect of the present invention, other than the inert gas (Ar, He, Kr, or the like) and nitrogen gas, a reactive gas (for example, oxygen, hydrogen, or the like) may be contained. The content of nitrogen contained in the mixture gas is preferably set at 20 to 80%. More preferably, it is desirable to set at 30 to 60%. In case of less than 20%, it is undesirable because the crystal grain diameter can not made fine, and if it exceeds 80%, it is undesirable because it becomes reduction of remarkable sputtering rate, reduction of coersive force by turning in of nitrogen to another layer, and aggravation of PW 50 value. Incidentally, in the vicinity of the content of nitrogen of 50%, the PW 50 value and the value of S/N ratio have optimal values.
Besides, for the above-described reason, the material of the substrate is preferably a glass substrate.
In the above recording medium of the present invention, the underlayer and the magnetic layer are not particularly limited.
The underlayer is formed for the purpose of improving the magnetic characteristics, and in case of the magnetic layer containing Co as the main ingredient, Cr single body or a Cr alloy is used. As the Cr alloy, CrV, CrW, CrMo, CrTi, or the like can be mentioned. The underlayer may be either of a singly layer and a plurality of layers.
As the magnetic layer, for example, a magnetic layer containing Co as the main ingredient such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt or CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtTaNb, CoCrPtTaB, or the like can be mentioned. The magnetic layer may be a multilayer constitution (for example, CoCrPtTa/CrMo/CoCrPtTa or the like) in which noise reduction is intended by dividing a magnetic film by a non-magnetic film (for example, Cr, CrMo, CrV, CrMnC, or the like), or a laminate structure in which the magnetic film is directly formed without interposing the non-magnetic film.
As the magnetic layer to cope with a magnetoresistive head (MR head) or a giant (large) magnetoresistive head (GMR head), a Co-base alloy containing an impurity element selected out of Y, Si rare earth element, Hf, Ge, Sn, and Zn, or oxides of these impurity elements, or the like is included. Besides, as the magnetic layer, other than the above, it may be ferrite-base, iron-rare earth-base, or granular in which magnetic grains of Fe, Co, FeCo, CoNiPt, or the like are dispersed in a non-magnetic film made of SiO2, BN, or the like. Besides, the magnetic layer may be either of recording forms of in-plane type and perpendicular type.
Besides, an intermediate layer for controlling the crystal orientation of the magnetic layer may be formed between the underlayer and the magnetic layer. As the intermediate layer, CoCr, CoCrNb, or the like can be mentioned.
On the magnetic layer, at need, a protective layer or a lubricating layer can be formed.
The protective layer is formed for the purpose of protecting the magnetic layer from being destroyed due to contact slide of a magnetic head. The protective layer can be formed from one layer or two layers or more. As the protective layer, a chromium film, a silicon oxide film, a carbon film, a hydrogenated carbon film, a nitrogenated carbon film, a hydro-, nitrogenated carbon film, a zirconia film, a silicon nitride film, a silicon carbide film, or the like can be mentioned. Incidentally, the protective film can be formed by a know film formation method such as a sputtering method or the like.
The lubricating layer is formed for the purpose of reducing the friction by contact slide with the magnetic head, and for example, perfluoropolyether or the like as a liquid lubricating agent is generally used.